System J-25 is a star system located in the Beta Quadrant, approximately 7,500 light years away from Federation space. The primary star of the system has been listed as FGC-J25 by the Federation. (ST reference: Star Charts)
In 2365, the USS Enterprise-D was flung into System J-25 by Q. Before setting a course for home, Captain Jean-Luc Picard ordered the Enterprise to perform a survey of the system, and discovered that several planets in the system were once inhabited, but now there was no signs of life, and evidence that the cities had been ripped from the surface in a manner similar to the outposts along the Romulan Neutral Zone.
As the Enterprise continued its research they were approached by a Borg cube. After both sides learned more about each others vessels, the cube suddenly attacked the Enterprise and caused severe damage as well as killing 18 crewmembers. Eventually, Picard pleaded with Q to send the Enterprise home, and he accepted. However, the Borg were now fully aware of the Federation and began making preparations for an invasion. (TNG episode: "Q Who?")